Method for expanding tobacco

ABSTRACT

Methods of expanding tobacco in which the tobacco is heated and moistened to increase the elasticity of the cell walls and then subjected to a vacuum rapidly imposed to convert moisture in the tobacco cells to vapor and effect an expansion in the volume of the moisture and a consequent distention of the cell walls to increase the size of cells. The tobacco is then frozen and dried in vacuo to remove at least part of the remaining water without significant alteration in the expanded structure of the tobacco. Heating to a temperature of at least -20* F. is then undertaken to sublime the remaining moisture.

United States Patent [191 Smith, Jr.

[ July 16, 1974 METHOD FOR EXPANDING TOBACCO [75] Inventor: Horace L.Smith, Jr., Richmond,

[21] Appl. No.: 321,226

Related U.S. Application Data [63] Continuation of Ser. No. 78,809, Oct.7, 1970,

abandoned.

[52] U.S. C1 131/140 P, 131/133 A [51] Int. Cl A241) 3/18 [58] Field ofSearch 131/138, 140 P, 144,

[56] References Cited UNITED STATES PATENTS 3,233,333 2/1966 Oppenheimer131/140 P UX 3,438,792 4/1969 Kruger 131/140 P UX 3,500,834 3/1970Taylor et al. 131/140 P 3,710,803 1/1973 Johnson 131/140 P 3,749,1037/1973 Abbott et a1. 131/140 P 3,785,385 l/l974 Johnson 131/140 PFOREIGN PATENTS OR APPLICATIONS 1,815,169 7/1969 Germany 131/140 P7/1952 Great Britain l3l/140 P OTHER PUBLlCATlONS Pages 8,9,10 and l lof Philip Morris German only are relied on.

Taylor et a1. is cited to show the use of radiant heat for freeze dryingof tobacco.

Primary ExaminerMelvin D. Rein Attorney, Agent, or FirmStrauch, Nolan,Neale, Nies & Kurz [57] ABSTRACT Methods of expanding tobacco in whichthe tobacco is heated and moistened to increase the elasticity of thecell walls and then subjected to a vacuum rapidly imposed to convertmoisture in the tobacco cells to vapor and effect an expansion in thevolume of the moisture and a consequent distention of the cell walls toincrease the size of cells. The tobacco is then frozen and dried invacuo to remove at least part of the remaining water without significantalteration in the expanded structure of the tobacco. Heating to atemperature of at least 20 F. is then undertaken to sublime theremaining moisture.

5 Claims, 2 Drawing Figures FREEZE Y MOISTURIZER VACUUM DRYER VACUUMCONVEYOR.

I CONVEYOR CONVEYOR PATENTEDJUL 1 SIM 823322,

SHEU 1 BF 2 HEATER MOISTURIZER FREEZE VACUUM DRYER CONVEYOR VACUUMCONVEYOR CONVEYOR FIG I PATENTEI] JUL 1 61974 SREUZUFZ METHOD FOREXPANDING TOBACCO This application is a continuation of US. Pat.application Ser. No. 78,809 filed Oct. 7, 1970 (now abandoned).

This invention relates to the treatment of tobacco and, moreparticularly, to the provision of novel improved methods of convertingtobacco to an expanded form.

One of the desired characteristics of cigarette tobacco is that thetobacco have a high percentage of voids. This minimizes the resistanceto the flow of air through the tobacco, making it easier to draw on thecigarette.

Also, as a tobacco having a high percentage of voids burns, an excess ofair over that needed for combustion is present in the combustion zone.The excess air reduces the temperature of the combustion products,providing the desired cool smoke."

Yet another advantage of a cigarette tobacco having a high percentage ofvoids is that the per cigarette content of nicotine and tars is low.Consequently, cigarettes made from such tobacco are safer to smoke thanthose made from tobacco having a lower void content.

Another desired characteristic of cigarette tobacco is that it have ahighdegree of structural integrity. This is necessary to produce thedesired firm cigarette in contrast to one which is soft or looselyfilled.

Conventionally, tobacco intended for cigarettes is shredded into narrowstrips to make the void content in the body of tobacco contained in acigarette as high as possible. However, conventionally produced shredsof tobacco are relatively limp and weak. When a body of tobaccoconstituted of such shreds is compressed to the extent required toproduce an acceptably firm cigarette, the void content is reduced to alevel well below that. which it would be preferable to employ. in otherwords, the physical characteristics of conventional cigarette tobaccosare such that the goal of high void content is incompatible with that offirmness.

It is also desirable that cigarette tobacco have as high a filling poweras possible. That is,'it is desired that the physical characteristics ofthe tobacco be such that a maximum number of cigarettes can be made froma given weight of tobacco since tobacco is purchased on a price perweight basis.

I have now discovered that cigarette tobacco having a high void content,a high degree of structural integrity, and high filling power can beproduced by subjecting conventionally processed tobacco to a process inwhich the tobacco is heated and/or moistened to increase the elasticityof the cell walls, subjected to a vacuum to convert moisture in thetobacco to vapor and effect an expansion in the size of the cells,frozen, and dried in vacuo to remove at least part of the waterremaining in the tobacco.

Because of the increase in cell size which results, tobacco producedinthe manner just described has a higher void content than conventionalcigarette tobacco. Also, by expanding the cell size, the thickness ofthe tobacco structure is increased, making it stiffer than conventionalcigarette tobacco. Consequently, a firm cigarette can be made fromtobacco treated by my novel technique without the necessity ofcompressing the tobacco to the heretofore'required extent. Accordingly,not only is the initial void content higher, but the in addition,because of its initial higher void content and the reduction incompression required to form a firm cigarette, tobacco treated in accordwith the present invention has higher filling power than conventionalcigarette tobacco; that is, a larger number of cigarettes can be madefrom-a given weight of tobacco.

Various techniques for expanding or puffing tobacco have heretofore beenproposed. Exemplary are those described in US. Pat. Nos. 1,789.434issued Jan. 20, 1931; 2,344,106 issued Mar. 14, 1944; 2,739,599 issuedMar. 27, 1956; 3,409,022 3,409,023, 3,409,027, and 3,409,028 issued Nov.5, 1968; 3,425,425 issued Feb. 4, 1969; and 3,524,451 and 3,425,452issued Aug. 18, 1970. However, to my knowledge, no one as heretoforedeveloped a process of expanding tobacco which has the dual advantagesof the process described above-increase in void content and increase inthe physical strength of the product.

The preferred apparatus for processing tobacco in accord with thepresent invention is of the continuous type and includes a vacuumconveyor into which conventional tobacco is introduced after the tobaccois first heated and/or moistened to increase the elasticity of the cellwalls. In this conveyor the tobacco is expanded by converting part ofthe moisture in it to vapor. As mentioned above, this increases thevolume of fluid in the cells of the tobacco, thereby distending thewalls of the cells and increasing their size. The tobacco is then cooledby auto-refrigeration while it is still in the vacuum conveyor to freezethe water remaining in the tobacco. Freezing the tobacco keeps the cellwalls from shrinking back to their original, unexpanded size.

From the vacuum conveyor the frozen tobacco passes into a vacuum chamberwhere water is sublimed from the tobacco by the application of radiantenergy until the moisture content of the tobacco is reduced to thedesired level. As the tobacco passes through the freeze dryer it isperiodically turned or tumbled or otherwise agitated vto exposedifferent surfaces of the tobacco to the radiant heat so that thetobacco will dry in a uniform fashion.

The use of freeze drying to dry the expanded tobacco is also animportant part of the present invention. By employing this technique,shrinkage of the cell walls is again avoided. Consequently, the driedproduct has the same desired expanded structure that the tobacco has atthe endof the step in which it is expanded.

From the freeze dryer the tobacco passes into a second vacuum conveyor.In this conveyor the pressure on and temperature of the tobacco areincreased to the ambient levels. As this occurs, any ice remaining inthe tobacco melts and diffuses through the treated tobacco, increasingits moisture content to the desired level. The tobacco is thendischarged from the vacuum conveyor to complete the process.

One important and primary object of the present invention resides in theprovision of novel improved methods of and apparatus for producingtobacco having a higher void content than conventional cigarettetobacco.

Another important and primary object of the invention is the provisionof novel methods of and apparatus able fines.

- the for producing tobacco which has greater strength or structuralintegrity than conventional cigarette tobacco.

Yet another related important and primary object of the invention is theprovision of novel, improved methods of and apparatus for producingtobacco which has greater filling power than conventional cigarette tobacco. 1

An important additional and primary object of the invention resides inthe provision of novel, improved processes of and apparatus forproducing expanded tobacco.

A related and important but more specific object of the inventionresides in the provision of methods of and apparatus for expandingtobacco in which the tobacco is heated and/or moistened to increase theelasticity of the cell walls, subjected to a vacuum to convert moisturein the tobacco to vapor and effect an expansion in the size of thecells, frozen, and dried in vacuo to remove at least part of the waterremaining in the tobacco without significant alteration of the expandedstructure of the tobacco.

Other important objects and features and further advantages of thepresent invention will become apparent from the appended claims and asthe ensuing detailed description and discussion of the inventionproceeds in conjunction with the accompanying drawing in which:

FIG. 1 is a flow diagram of apparatus for treating tobacco in accordwith the principles of the present invention; and

FIG. 2 is a partially diagrammatic illustration of certain majorcomponents of the apparatus of FIG. 1.

As discussed briefly above, in the novel process of expanding tobaccodescribed herein the tobacco is first heated or moistened or preferablyboth heated and moistened to increase the elasticity of the walls of thecells in the tobacco. Cured tobacco has a very low moisture content andis very brittle. In this state the tobacco can not be satisfactorilyexpanded as the cells will simply rupture instead of distending.Attempts to expand tobacco in the typical cured state typically resultnot only in a lowdegree of expansion but considerable shattering and aconsequent production of unus- As the temperature and moisture contentof the tobacco are increased, gums, oils and other constituents becomeless viscous; and the walls of the tobacco cells become more flexible.The tobacco cells can then be expanded without rupturing the walls ofthe cells.

Both the temperature to which the tobacco is heated and the level towhich its moisture content is adjusted will vary considerably, dependingupon a number of factors. These include the extent to which the tobaccois to be expanded; the physical form of the tobacco-leaves (whichinclude stems and veins); strips (leaves without veins); or cut filler(strips shredded for cigarette making and usually mixed with particlesof stems and veins); the particular variety or blend being processed;and others. The tobacco may, however, be heated to temperatures up to170 F. sinceeven the least robust tobaccos can be heated to thistemperature for the limited times involved without impairment of flavoror colonNevertheless, in a typical application of invention, a somewhatlower temperature (l30l50 F.) will preferably be employed.

The addition of even large amounts of water to tobacco for short periodsof time does not appear to have a detrimental effect on the tobaccoalthough excessive water may make the tobacco difficult to handle.Accordingly, there does not appear from this point-ofview to be acritical upper limit on the level to which the moisture content of thetobacco is increased in the initial steps of the tobacco expandingprocess I have invented. However, in a typical application of theinvention, it will not prove necessary to add to the tobacco more thanO.l50.2 pounds of water per pound of tobacco.

The next step in the novel process I have invented is to rapidly reducethe pressure on the heated and/or moistened tobacco to a levelsufficiently low that a part of the moisture in the cells of the tobaccowill vaporize. As this occurs, the volume of moisture increasesenormously. As a consequence, the walls of the cells are distended,expanding the size of the cells.

The level to which the pressure on the tobacco is reduced is a parameterwhich will vary from applicationto-application of the invention. In atypical application, however, the pressure on the tobacco will bereduced to on the order of one pound per square inch absolute togenerate the vapor required for expansion of the tobacco.

The vaporization of the moisture in the tobacco is accompanied by adecrease in the temperature of the tobacco since the tobacco and themoisture it contains supply the latent heat of vaporization. In somecases this temperature decrease may be sufficiently large to decreasethe elasticity of the cell walls to an undesirable extent. Also, theevaporation of moisture from the tobacco in the expansion step mayreduce the moisture content to an undesirably low level.

In such cases steam is added to the tobacco in the novel process I haveinvented. The steam keeps the temperature of the tobacco at the desiredlevel and also reduces the loss of moisture from the expanding tobacco.The temperature and pressure of the steam used for this purpose as wellas the amount which is. used will of course depend on a number offactors including the amount of heat required to keep the tobacco at thedesired temperature level, the moisture content of the steam, etc.

Atthe end of the expansion step, the tobacco is still in a relativelyplastic state; i.e., the cell walls are still relative elastic. To keepthe tobacco from shrinking back toward its unexpanded state, themoisture remaining in the tobacco is promptly frozen.

The freezing step is accomplished by further reducing the pressure onthe tobacco, typically to a pressure on the order of 0.02 to 0.04 psia.At such pressures water can exist only in the form of ice at thetemperature which the tobacco will typically have. Accordingly, as thepressure on the tobacco is reduced to these levels, ice is formed in thecells of the tobacco to keep them from shrinking. Also, the gums, oils,and similar constituents in the tobacco become extremely viscous and thecell walls lose elasticity, further assisting in keeping the tobacco inthe expanded state.

Moisture must be removed from the frozen tobacco to reduce its moisturecontent to the level which is desired in the expanded tobacco. This isaccomplished in accord with the present invention by keeping the frozentobacco under a high vacuum and heating it, preferably by'theapplication of radiant heat. This causes moisture remaining in thetobacco to sublimate; i.e., to pass directly from the solid to thegaseous state.

The advantage of drying the expanded tobacco in the manner justdescribed is that the removal of excess moisture can be accomplishedwithout significant alteration in the expanded characteristics of thetobacco. Accordingly, the use of the just described technique (commonlyreferred to as freeze drying) to dry the expanded tobacco is consideredan important part of the present invention.

The tobacco is preferably turned or tumbled periodically during thedrying step. This promotes uniformity in the exposure of the differentsurfaces of the tobacco to the radiant heat and, consequently, uniformdrying.

Normally, it is desired that the expanded and dried tobacco have adefinite, predetermined moisture content; i.e., that it not be reducedto a bone dry state. This keeps it from being too brittle, reduces itsburning rate, etc. Accordingly, the freeze drying step is normallyterminated while there is still some ice in the tobacco. The tobacco isthen returned to ambient conditions. As this occurs, the ice melts, andthe resulting water diffuses through the tobacco, increasing itsmoisture content to the desired level. c

Referring now to the drawing, FIG. 1 illustrates in block diagram formapparatus for expanding tobacco in accord with the principles of thepresent invention. The first major component of apparatus 10 is a heater12 in which the temperature of the tobacco to be expanded is increased.I

This is to lower the viscosity of gums, oils, and similar constituentsof the tobacco and to increase the flexibility of the tobacco cell wallsso that the tobacco may be expanded without rupturing or shattering thewalls of the tobacco cells. i

' ofthe present invention, they will not be described fur- Afterheating, the tobacco may be expanded. Typically, however, it will firstbe delivered to a moisturizer 14 to increase the moisture content of thetobacco. As discussed above, this also increases the elasticity of thewalls of the tobacco cells, making the tobacco easier to expand. I V iFrom heater 12 (or moisturizer 14), the tobacco is delivered to a vacuumconveyor 16 in whichthe now elastic tobacco is expanded and then frozento prevent it from shrinking toward its unexpanded state. The vacuumconveyor then delivers the frozen tobacco to a freeze dryer 18, whereexcess moisture is removed from the tobacco. The dried tobacco isdischarged into a second vacuum conveyor 20 in which the temperature ofand the pressure onthe tobacco increases to the ambient level. As thisoccurs, any ice remaining in the expanded and dried tobacco melts; andthe water diffuses throughout the tobacco, increasing its moisture 1content to the desired level. From this vacuum conveyor, the tobacco isdischarged onto a conventional transfer conveyor 22, which conveys thedried, expanded tobacco to a cigarette making machine orother station(not shown) for further processing.

Heater l2 and moisturizer 14 may be of any desired construction and may,in fact, advantageously be combined into a single unit in manyapplications of the present invention. Suitable units capable ofconcomitantly heating and increasing the moisture content of tobacco aredisclosed in my prior U.S. Pat. Nos. 2,086,446 issued July 6, 1937;2,124,012 issued July ther herein.

As indicated above, the heated and/or moisturized tobacco flows fromheater 12 or moisturizer 14 to vacuum conveyor 16 in which the tobaccois first expanded and then frozen to eliminate shrinkage. Referring nowto FIG. 2, the preferred form of conveyor includes an elongated,cylindrical casing 24 through which an endless, flexible chain 26extends. Chain 26 also extends through an elongated cylindrical guide 27disposed in parallel, spaced relationship to casing 24.

Fixed to endless chain 27 atv substantially equidistantly spacedintervals are pistons 28 which are circular discs or flights configuredto engage the inner wall 30 of casing 24. Peripheral seals on flights 28(not shown) will generally be employed to keep gas from leaking past theseals. Preferably, the distance between pistons 28 is so related to thelength of casing 24 that there are always plural pistons in the casing.This provides plural seals between vacuum dryer l8 and the surroundingenvironment to minimize leakage into the freeze dryer.

Also, the interior of casing 24 may be coated with Teflon or othermaterial having a low coeffecient of friction or otherwise treated toreduce sliding friction between casing 24 and the flights 28 of conveyor16.

Belt 26, which consists of links 32 connected by pivot or hinge pins 24,is trained around sprocket members 36 and 38 at opposite ends of casing24. The sprockets are rotated in the directions indicated by arrows 40and 42 in FIG. 2 by a drive arrangement of appropriate construction (notshown). As the sprockets rotate, the connecting pins 34 of belt 26 aredrivingly engaged in recesses 44 at the outer ends of sprocket arms 46.Accordingly, as they revolve, the sprockets propel drive chain 27 andflights 28 through cylindrical casing 24 in the direction indicated byarrow 48 in FIG. 2. It will be apparent from FIG. 2 and from theforegoing description that pistons '28 cooperate with casing 24 to forma series of moving, substantially gastight com- .partments 50. Thesecompartments are filled with the tobacco to be expanded after it hasbeen heated and/or moisturized from a hopper 52 which communicates withthe interior of casing 24 adjacent the feed end of the latter.

4 Intermediate its ends, the interior of casing 24 is connected througha conduit 54 to a vacuum pump 56. Ac-

, cordingly, as each compartment 50 moves through casing 24,communication is established between it and vacuum pump 56 to reduce thepressure on the tobacco in the compartment.

As discussed above, the pressure is reduced to a sufficiently low valuethat part of the moisture in the tobacco will be converted to watervapor. This enormously increases the volume of the moisture; and thevapor accordingly distends the more-or-less elastic walls of the tobaccocells, thereby expanding the size of the cells. By controlling the speedof conveyor belt 26, the rate of conversion of the moisture in thetobacco to water vapor can be regulated so that the vapor will be formedfast enough to effect the desired expansion but not so fast'as toexplode the tobacco.

The vaporization is accompanied by a drop in the temperature of theexpanding tobacco clue to the loss of latent heat of vaporization. Asdiscussed above, this may in some cases result in an unacceptabledecrease in the elasticity of the tobacco. It was also pointed out thatthe temperature drop can be offset by adding steam to the tobacco as itexpands. Provision is made for this in the apparatus shown in FIG. 2.More specifically, a steam line 58 is connected to the interior ofcasing 24 at approximately the same location or station as vacuum line54. A valve 60 in steam line 58 can be opened to admit steam to theinterior of the casing as needed.

In addition to water vapor, non-condensible gases (primarily air) willbe present in each compartment 50 during the expanding step. As thevapor is formed and exits from casing 24 through vacuumline 54, itentrains the non-condensible gases, evacuating them from the compartment50 in communication with the vacuum line through the latter. Referringstill to FIG. 2, downstream of the station at which vacuum line 54 andsteam line 58 communicate with the interior of casing 24, a secondvacuum line 62 is connected to the interior of the casing. Vacuum line62 is connected through a second vacuum line 64 to a condenser 66 whichwill be described in more detail later. Vacuum line 62 is provided sothat the pressure on the non-expanded tobacco can be further decreased.Valve 65 in line 62 can be adjusted toregulate the extent to which thepressure on thetobacco is reduced.

More specifically, as discussed above, after the expansion step iscompleted, the pressure on the expanded tobacco is reduced to a level atwhich additional moisture will convert into vapor. This extractsadditional heat from the tobacco, causing the remaining moisture tofreeze. The freezing of the expanded tobacco eliminates shrinkage byincreasing the viscosity of gums, oils, and other constituents in thetobacco; by reducing the flexibility ofthe tobacco cell walls; and byforming ice in the cells of the tobacco to keep them from contracting.

At the right-hand end of conveyor casing 24 as shown in FIG. 2, theexpanded, frozen tobacco is discharged from the casing through avtransfer conduit 68 into freeze dryer 18. As shown in FIG. 2 the freezedryer includes a generally gastight casing 70 housing a series ofconventional, horizontally oriented, vertically spaced apart conveyors72, 74, 76 and 78. Each of these conveyors includes an endless belt 80trained around rol lers 82 and 84, one or both of which may be driven byan appropriate drive arrangement (not shown).

The three lower conveyors 74, 76, and 78 are so positioned relative toeach other and to conveyor 72 that the feed end of each conveyor ispositioned below the discharge end of the conveyor thereabove.Accordingly the expanded, frozen tobacco falls through transfer conduit68 onto the feed end of conveyor 72. It pro ceeds along conveyor 72 andthen passes over the discharge end of the latter onto the feed end ofconveyor 74, proceeds along the latter, falls onto the feed end ofconveyor '76, etc. Finally, the material is discharged from conveyor 78through transfer conduit 86 into the discharge vacuum conveyor 20.

fresh surfaces to radiant heat emanating from radiators 88 disposedclosely adjacent the upper runs of the conveyors. This promotes uniformexposure of the tobacco surfaces to the radiant heat and, consequently,uniform drying of the tobacco.

Radiators 88 may be of any desired type such as, for example, thosedisclosed in my U.S. Pat. Nos. 3,262,494 issued July 26, 1966; 3,285,514issued Nov. 15, 1966; and 3,305,011 issued Feb. 21, 1967.

The interior of vacuum vessel 18 is maintained at a pressure typicallyon the order of 0.04 inch of mercury absolute. At this pressure theexcess moisture in the frozen tobacco will, upon the application of heatfrom radiators 88, pass directly from the frozen state to the vaporstate;'i.e., sublime, at temperatures of 20 F. or higher. The heat fromradiators 88 increases the tobacco temperature to a higher level toeffect sublimation of the excess moisture from the frozen tobacco.

This method of removing excess moisture is an important part of thepresent invention since it permits the moisture to be removed withoutsignificant shrinkage of the expanded tobacco. By the time the tobaccois dried'to a typical final moisture content, elasticity of the cellwalls of the tobacco is reduced and the viscosity of the gums, oils, andthe like increased to such an extent that shrinkage is no longer aproblem.

Radiators 88 are heated by circulating a fluid, preferably liquid, heattransfer medium through them. Suitable heat transfer liquids, capable ofbeing heated to temperatures as high as 800 F. without an unacceptablyhigh rate of degradation, are disclosed in my U.S. Pat. No. 3,236,292issued Feb. 22, 1966.

Radiators 88 are incorporated in a liquid heating and circulation system90. In addition to the radiators, this system includes a heating unit92. The heating unit is connected to the radiators by supply conduit 94,supply header 96, and branch supply conduits 98 and by branch returnconduits 100, return header 102, and mainreturn conduit 104. A pump 106in main return conduit 104 circulates the heat transfer medium throughthe closed system just described. Flow through each of the radiators 88is regulated by a valve 108 in the associated" branch supply conduit 98so that the heat from each radiator to the tobacco on the associatedconveyor can be'independently controlled.

The heating system just described will in actual practice include anumber of additional components as will be apparent to those versed inthe arts to which this invention relates. However, as such componentsare not part of the presentinvention and as they are described in U.S.Pat. No. 3,236,292 and elsewhere, they will not be referred to furtherherein.

It is necessary to continuously remove the evaporated moisture fromvacuum vessel since, at typical operating pressures and temperatures,each pound of water removed from the tobacco occupies several thousandcubic feet. One form of apparatus which may be employed for this purposeincludes the condenser 66 referred to above. The condenser is connectedto vacuum vessel 70 by the above-mentioned conduit 64 and by conduit 110and to a vacuum pump 112 by conduit 114. A valve 115 regulates the flowthrough conduit 110 to the-condenser.

Vacuum pump 112, which is also used to pump down vacuum vessel 70 whenthe system is started up, draws the accumulated water vapor from vacuumvessel 70 through conduits 110 and 64 and upwardly through condenser 66,where it is absorbed by a refrigerated sorbent such as an aqeuouslithium chloride solution. The sorbent is pumped from a conduit 116 intothe upper end of condenser 66 and flows downwardly through the condenserover interleaved horizontal baffles 118.

From the lower end of the condenser the sorbent, heated and diluted byabsorbed water vapor,-flows through conduit 120 into pump 122, whichcirculates the diluted sorbent through conduits 124 and 126 into thecooler 127 of refrigeration apparatus 128, which also includes arefrigeration producer 129a connected to cooler 127 by conduits 12912and l29c. The refrigeration apparatus may be of any appropriate typesuch as the ammonia compression system disclosed in my U.S. Pat. No.2,515,098 issued July 11, 1959. In cooler 127 the lithium chloridesolution is cooled'for recirculation to condenser 66. As therefrigeration system is per se not part of the present invention and assuitable systems can be readily selected by those familiar with therelevant arts, this system will not be described further herein.

A second, smaller circulating pump 130 continuously draws a portion ofthe dilute solution from conduit 124 and delivers it through conduits132 and 134 to a sor-.

bent concentrator or reboiler l36,'which may be of the type described inmy U.S. PatuNo. 2,515,098. Here, excess water is boiled off the sorbentsolution to increase its concentration.

From reboiler 136, the sorbent flows through conduit 138, a coil 140 inheat exchanger 142,.and conduit 144 back into refrigeration unit cooler127, where it is cooled for recirculation to condenser 66. As the hot,concentrated sorbent flows through heat exchanger 142, it gives upotherwise unusable sensible heat to dilute sorbent flowing to reboiler136 through a coil 146 disposed in heat exchanger 142 in heat transfer.relationship to coil 140. Circulation of the sorbent from main returnconduit 124 through the reboiler and flow of the concentrated sorbentfrom the reboiler through heat exchanger 142 to refrigeration unit 127are controlled by valves I48 and 150 in conduits 132 and 138,respectively.

The details of the vapor removal system just described are not criticalin the practice of the present invention. For this reason and becauseappropriate systems are discussed in detail in my U.S. Pat. No.2,515,098 and in my cope'riding U.S. Pat. application No. 69,497 filedAug. 6, 1970, both of which are hereby incorporated by reference, thissystem will not be discussed furtherherein.

Referring again to FIG. 2, the vacuum conveyor into which the driedtobacco is transferred from freeze dryer 18 is of essentially the sametype as the vacuum conveyor 16 discussed above. This conveyor includes acylindrical casing 152 through which an endless belt 154 consisting oflinks 156 connected by hinge pins 158 extends. Belt 154 also extendsaround sprockets 160 and 162, which drivingly engage the belt in themanner described above, and through a cylindrical guide 164.

Fixed to endless belt 154 at generally equidistantly spaced intervalsare pistons 166 in the form of circular discs or flights which areconfigured to match the inner wall 167 of casing 152 and carryperipheral sealing members (not shown) to provide generally gastightseals between the flights and the interior of the casing. Also, as inthe case of conveyor 24 and for the same reasons, the conveyor ispreferably constructed so that there are always plural pistons in casing152 to isolate freeze dryer 18 from the surrounding environment. And, asin the caseof conveyor 24, the interior of the casing may be coated withTeflon or the like to reduce sliding friction between'the casing andconveyor flights 164.

Sprockets and 162 are rotated in the directions indicated by arrows 168and 169 in FIG. 2 by a suitable drive mechanism (not shown).Accordingly, conveyor flights 166'cooperate with the interior of casing152 to form a series of pockets 170 which move through casing 152 in thedirection indicated by arrow 172 in FIG. 2. Compartments 170 are filledwith dried tobacco from transfer conduit 86 and carry the tobaccothrough the conveyor from right to left as shown in FIG. 2.

In a typical application of the present invention, only a part of themoisture present in the tobacco is removed in freeze dryer 18, theremaining moisture being in the form of ice as the tobacco istransferred into discharge conveyor 20. As the tobacco is moved throughconveyor 20 in pockets 170, the pressure on and temperature of thetobacco is increased. The remaining ice accordingly melts, and theresulting water diffuses, throughout the tobacco. In this manner, themoisture content of the expanded product can be adjusted to any desiredlevel.

As shown in FIG. 2, the interior of casing 152 is connected throughvacuum line 174 to a vacuum pump 176 adjacent the right-hand end of thecasing. Vacuum pump 176 keeps air and other non-condensibles enteringcasing 152 at the right-hand end thereof from flowing into the freezedryer 18.

From the left-hand end of conveyor 20 the expanded tobacco is dischargedthrough conduit 178 onto transfer conveyor 22. As discussed above, thisconveyor transfers'the expanded tobacco to a cigarette making machine orother station for further processing.

The invention may be .embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. The method of expanding tobacco, comprising the step of heating thetobacco to a temperature of not more than 170 F. and concurrentlymaintaining moisture in said tobacco at a selected level of not morethan 0.2 pounds of water per pound of tobacco to thereby increase theflexibility of the cell walls of said tobacco, the pressure on saidtobacco being kept sufficiently high during said step to keep the waterin the tobacco in the liquid state; reducing the pressure on said heatedand moistened tobacco after the cell walls thereof have become plasticto a subatmospheric level of not more than about 1 pound per square inchabsolute with sufflcient rapidity to cause a part of the water in saidtobacco to flash from liquid into vapor, thereby increasing its volumeand effecting an expansion in the sizes of the cells in said tobacco;thereafter freezing the water remaining in the tobacco to keep the cellsin said tobacco from shrinking by reducing the pressure on said tobaccoto a level of not more than 0.04 pounds per square inch absolute; andthereafter drying the tobacco to reduce the moisture content of thetobacco to a selected level without significantly altering the expandedphysical structure of the tobacco by maintaining the pressure on thefrozen tobacco at said lower level and heating the moisture in thetobacco to a temperature of at least F. to sublime excess moisture fromthe tobacco.

2. The method of-claim 1, together with the step of adding steam to thetobacco as the pressure thereon is reduced to thereby maintain thetemperature and moisture content of the tobacco sufficiently high tokeep the cell walls of the tobacco elastic while said tobacco isexpanded.

3. The method of claim 1, together with the step of heating the driedtobacco to melt the ice remaining therein and thereby adjust themoisture content of said tobacco to a selected level.

4. The method of claim 1, wherein the moisture in said tobacco ismaintained at said selected level by adding water thereto in an amountsufficient to increase said moisture content to said level and whereinthe pressure on the tobacco during the addition of the water is'keptsufficiently high to keep the added water in the liquid state.

5. The methodof expanding tobacco, comprising the step of heating thetobacco to a temperature of not more than F. and concurrently addingwater to said tobacco in an amount sufficient to increase the level ofmoisture therein to a selected level of not more than 0.2 pounds ofwater per pound of tobacco to thereby increase the flexibility of thecell walls of said tobacco, the pressure on said tobacco being keptsufficiently high during the addition of said water to keep the water inand added to said tobacco in the liquid state; reducing the pressure onsaid heated and moistened tobacco after the cell walls thereof havebecome plastic to a sub-atmospheric level of not more than about 1 poundper square inch absolute with sufficient rapidity to cause a part of thewater in said tobacco to flash from liquid into vapor, therebyincreasing-its volume and effecting an expansion in the sizes of thecells in said tobacco; thereafter freezing the water remaining in thetobacco to keep the cells in said tobacco from shrinking by reducing thepressure on said tobacco to a lower level of not more than 0.04 poundsper square inch absolute; and thereafter drying the tobacco to reducethe moisture content of the tobacco to a selected level withoutsignificantly altering the expanded physi- 90-1050 miss s'm'rss mime:@FlltE CERTIFICATE @F CORRECT-Mm Patent No. 3,823,722 mess Jul is 1.974

EWEMDMS) HoraceL. Smitm Jr.

It is certified that err-exappears in the above identified patent andthat said Letters Patent are hereby corrected as shown below:

the the diselesute t0 read es Methods of expanding tebaeeo in which thetobaeee is heated amfi moistened to increase the elestieity of the cellwalls and then subjected te e vacuum rapidly im posed to eenvertmoisture in the tobacee cells vaper and effect an expansion in thevolume oi the moisture anti consequent distention of the cell walls toincrease the size of cells. The tobacco is then frozen and dried invacuo and at a temperature of at least 20" F0 to sublime at least partof the remaining water without significant alteration in the expandedstructure of the tObaCCO,-

Column 2 line 1.41, change "1,7s9434" to --1 ,7a9 434--. Column 3, line4:4 after Haunt insert --in--=-w ,Column 6, line 19, change "27" to=--26--.,

I Column 6,, line 35, change 24" to --34--.

Column 6, line 42 change "27" to --=-26--J Column 9, line 53, ehange"69,497" to -=-6l,'772--2 after "1.970 insert (now Patent No, 3,62l 587,issued November 23, 19710-- Celumn 11, line 6; before "level insert--lower--,

and sealed this 26th day of November 2,9743% Attests lfeCOY Mo GIBSGNJR? Ce MARSHALL DAN??? ettesting Gffieer Cenmissiemer ef Patents

1. The method of expanding tobacco, comprising the step of heating thetobacco to a temperature of not more than 170* F. and concurrentlymaintaining moisture in said tobacco at a selected level of not morethan 0.2 pounds of water per pound of tobacco to thereby increase theflexibility of the cell walls of said tobacco, the pressure on saidtobacco being kept sufficiently high during said step to keep the waterin the tobacco in the liquid state; reducing the pressure on said heatedand moistened tobacco after the cell walls thereof have become plasticto a subatmospheric level of not more than about 1 pound per square inchabsolute with sufficient rapidity to cause a part of the water in saidtobacco to flash from liquid into vapor, thereby increasing its volumeand effecting an expansion in the sizes of the cells in said tobacco;thereafter freezing the water remaining in the tobacco to keep the cellsin said tobacco from shrinking by reducing the pRessure on said tobaccoto a level of not more than 0.04 pounds per square inch absolute; andthereafter drying the tobacco to reduce the moisture content of thetobacco to a selected level without significantly altering the expandedphysical structure of the tobacco by maintaining the pressure on thefrozen tobacco at said lower level and heating the moisture in thetobacco to a temperature of at least 20* F. to sublime excess moisturefrom the tobacco.
 2. The method of claim 1, together with the step ofadding steam to the tobacco as the pressure thereon is reduced tothereby maintain the temperature and moisture content of the tobaccosufficiently high to keep the cell walls of the tobacco elastic whilesaid tobacco is expanded.
 3. The method of claim 1, together with thestep of heating the dried tobacco to melt the ice remaining therein andthereby adjust the moisture content of said tobacco to a selected level.4. The method of claim 1, wherein the moisture in said tobacco ismaintained at said selected level by adding water thereto in an amountsufficient to increase said moisture content to said level and whereinthe pressure on the tobacco during the addition of the water is keptsufficiently high to keep the added water in the liquid state.
 5. Themethod of expanding tobacco, comprising the step of heating the tobaccoto a temperature of not more than 170* F. and concurrently adding waterto said tobacco in an amount sufficient to increase the level ofmoisture therein to a selected level of not more than 0.2 pounds ofwater per pound of tobacco to thereby increase the flexibility of thecell walls of said tobacco, the pressure on said tobacco being keptsufficiently high during the addition of said water to keep the water inand added to said tobacco in the liquid state; reducing the pressure onsaid heated and moistened tobacco after the cell walls thereof havebecome plastic to a sub-atmospheric level of not more than about 1 poundper square inch absolute with sufficient rapidity to cause a part of thewater in said tobacco to flash from liquid into vapor, therebyincreasing its volume and effecting an expansion in the sizes of thecells in said tobacco; thereafter freezing the water remaining in thetobacco to keep the cells in said tobacco from shrinking by reducing thepressure on said tobacco to a lower level of not more than 0.04 poundsper square inch absolute; and thereafter drying the tobacco to reducethe moisture content of the tobacco to a selected level withoutsignificantly altering the expanded physical structure of the tobacco bymaintaining the pressure on the frozen tobacco at said lower level andheating the moisture in the tobacco to a temperature of at least -20* F.to sublime excess moisture from the tobacco.